Process and apparatus for grinding cereal grains



Dec. 28, 1965 H. GRAUMANN 3,226,041

PROCESS AND APPARATUS FOR GRINDING CEREAL GRAINS Filed Sept. 19, 1965 United States Patent 3,226,041 PROCESS AND APPARATUS FOR GRINDING CEREAL GRAINS Hermann Graumann, Heiloo, Netherlands, assignor to Lavasto S.A., Geneva, Switzerland Filed Sept. 19, 1963, Ser. No. 310,031

Claims priority, application Netherlands, Sept. 27, 1962,

283,721 7 Claims. (Cl. 241-9) This invention relates to a process and apparatus for grinding cereal grains, such as wheat and rye and like shell covered fruits.

The purpose of the usual grinding process in grain milling is the production of grit, dust and flour by reducing the size of the cereal grain and by separating the kernel representing the flour portion of the grain from the shell envelope in order to extract the important components which contain the physiologically nutritious values, namely starch and albumen, and to separate these latter components from the shell portions which have a disadvantageous effect on the nutritious value, and if possible without any loss of the nutritious components.

In view of the fact that the envelope of the kernel, namely the shell, has in comparison to the flour kernel or endosperm a relatively high content in ashes or mineral substances, the purpose of the grinding process is to obtain a product of the above mentioned type which is as much as possible without these shell ashes.

In order to provide such a product, a grinding process is necessary which reduces the flour body of the grain to the desired fineness or grain size on the one hand, and which, on the other hand, prevents a too extensive crushing or cutting of the shell components in order to separate them after their detachment or loosening from the endosperm particles, which should be as complete as possible, by means of suitable sifting or separating processes.

The processes for reducing the size of the grains employing impact, cutting or friction tools are inappropriate for accomplishing such a grinding action because they crush or comminute simultaneously with the flour body or endosperm also the shell components to a more or less extensive degree.

It is to be noted, however, that the prior art crushing or comminuting apparatus employed in grain milling employ such processes and devices in a more or less pronounced form. This circumstance has caused a development of very long, multiple-step grinding processes, whose individual Working steps are simultaneously directed to preserving the envelope of the kernel or its components to a large extent. These processes may be subdivided into three main steps, namely:

(1) the rough grinding,

(2) the separation; and

(3) the grinding out or full grinding.

The rough grinding is the first grinding step carried out on chamfered roller pairs, whose individual rollers rotate at a different relative speed. They comminute or cut the grain first into four parts which are separated during a subsequent sifting operation according to their size as follows:

(a) The coarse grit which comprises the larger particles in excess of about 750 microns to which the shell particles are still attached, and comprising also shell particles which are more or less detached from the endosperm, and of the same size;

(b) The grit which consists of fragments of the endosperm of finer size, approximately between 350 and 750 microns, which are in part clean and in part still attached to shell portions;

3,226,041 Patented Dec. 28, 1965 (c) The grit dust which consists of partices in the size of from about to 350 microns and generally of the same composition as the grit semolina; and

(d) The grit flour or fine flour constituting the portion of the ground meal obtained which contains the finest particles, derived from the endosperm, but which due to the particular type of comminuting or cutting process, is mixed to a more or less great extent with shell particles of the same size and which can no longer be removed by the known sifting or separating processes. This grit flour or meal thus constitutes already a part of the finished product.

Further grinding or grit producing processes, generally four to six such processes have the purpose of further reducing the coarse grit obtained during the first grinding step, again employing chamfered rollers While attempting to preserve the shell to a large extent as described above, until the remaining shell components are removed to a larger or smaller degree from the endosperm.

Before the grit semolina is in turn ground further, it is separated on so called grit cleaning machines first from the shell fragments which are more or less free of endosperm, and which cannot be separated by the usual sifting process. The grit semolina cleaned on these machines is then divided in the next grinding step, also in a stepwise reduction, into dust and flour. This work process is carried out usually on smooth roller pairs whose individual rollers rotate also at difierent peripheral speed. This step is characterized thus by a crushing and grinding action. During this crushing process between the smooth rollers the pressure upon the grains in passing between the rollers causes them to be transformed into flat bodies or cakes, that is a grinding product which is coherent due to its physical nature although it has been pulverized. These small plate-like bodies are then separated in disengaging apparatus by a pressing of the product through an annular slit or in a centrifugal machine by impact or thrust effect before being separated in the subsequent sifting process into the above mentioned fractions, namely dust and flour.

The dust portion as well as the grit dust is separated previousy also on grit cleaning machines from shell fragmens of the same size which are more or less free of endosperm particles, are now ground in the above mentioned third grinding phase, the so-called grinding-out step, also on smooth rollers rotating at different peripheral speeds in the same manner as described above to obtain a flour of the desired grain size and again in a long, step-wise working process, in order to be able to prevent here also as much as possible a pulverizing of the shell components which are still attached, so as to be able to separate them in the sifting process which usually follows.

The grinding tools of this entire crushing process consist thus of chamfered as well as of smooth roller pairs, and their mode of operation is basically characterized by the different peripheral speeds of the individual rollers of each roller pair. The form and number of the chamfers or grooves as well as their turn or twist, that is their position relative to the roller axis, are quite different depending on their predetermined crushing or cutting purpose, or depending on the type and physical nature of the particular cereal grain to be milled. However, the differential speed of the roller pairs, that is to say the difference in the relative peripheral speeds is much less pronounced in the individual milling purposes. For example in the coarse grinding of rye it is in the range of 1:3, of wheat in the range of 1:2,5 and during the separating and grinding out process in the range of 4:5.

Thus the crushing is carried out in the course of the entire grinding process in the grain milling art partly by means of the cutting and crushing effect of the chamfers 3 and partly by the crushing and wearing effect of the smooth rollers.

This grinding process causes in spite of the most careful work in regard to preventing to a large extent any simultaneous grinding of the shell components due to the cutting and crushing operation nevertheless to a substantial degree a comminuting to a maximum particle size of about 150 microns which corresponds to that of the flour. These shell particles can no longer be separated by sifting or other processes from the flour produced and increase thus to a more or less high degree the ash content of the flour thereby affecting also adversely its utilitarian value.

More recently one has employed also for the separating and grinding-out steps instead of smooth roller pairs with a peripheral speed difference of 4:5 as indicated above, so-called grinding out machines. They consist of a pair of smooth rollers rotating at the same or approximately the same peripheral speed, so-called sizing rollers, and a roller of artificial stone mounted thereafter, which rotates in contact with a stationary grinding segment of the same material and with a more or less intense pressure. The simultaneous crushing and wearing effect of the grinding process of the usual smooth roller pairs is merely divided in this type of grinding machine into two separate succesive working processes which could also be called a pressure without friction and friction without pressure. In this case the smooth rollers have only a preparatory purpose. The friction effect is thus an essential component also of the crushing process of these grinding-out machines. A grinding of shell components cannot be avoided here and they are ground to a size which makes the separation from the flour by customary sifting processes impossible. Therefore the flour obtained with this type of apparatus does not present a lower ash content, but in many instances even a higher ash content than with apparatus comprising smooth roller pairs with the usual successive separating machines.

The long, step-wise crushing process described above with the additional devices and processes required, such as grit-cleaning and ventilating of the individual machines and the like, requires a considerable investment in machines and apparatus. Furthermore, considerable heat is developed in this type of grinding operation due to the above-mentioned type of operation of the grinding tools. This heat is transferred partly to the machinery and partly to the material being ground as far as it is not removed by a corresponding ventilation and perhaps a special cooling of the rollers, in order to avoid above all an excessive heating of the grinding product. The grinding heat brings about also a considerable evaporation of the humidity contained in the grains, which in turn causes in the ventilating and pipe system of the entire grinding installation often disturbing condensation phenomena, and thus may adversely alfect the operating process and the proper working of the sifting apparatus. This in turn necessitates much expense in controlling the entire working process of the grinding operation.

Due to the temperatures developed during this crushing in spite of the meaures to produce a cooling of the grinding machinery and of the grains, particularly during the warm season and in tropical countries, the resulting product is heated to such an extent that its storing property or shelf life is impaired.

In wheat and rye milling there is particularly the additional danger of injury to the starch of the endosperm by the repeated friction process in an extended grinding operation, and thus of impairing the useful properties of the flour produced. The grinding heat and the different systems designed to carry away the heat also take up a considerable portion of the energy consumption necessary for the grinding process.

By way of many tests it has now been found that a grinding of cereal grains and similar grain fruits comprising the coarse grinding as well as the separation and grinding-out processes, may be carried out exclusively on smooth roller pairs whose individual rollers rotate at the same speed relative to each other, thus without any cutting or friction effect, so that undesirable and disadvantageous factors accompanying the present operations may be avoided to a large degree. The size reduction of the grains is obtained merely by a crushing or crumbling of the grains between the rollers.

The structure of the endosperm is greatly deformed in the desired amount by the particular distance at which the rollers are set relative to each other. By the pressing or crumbling of the grains in passing between the rollers a portion thereof is obtained in the form of small plates or cakes which consist of individual particles which form a coherent body due to their physical nature. By means of a centrifugal process in a so-called centrifugal separa tor as employed already in the cereal milling art as indicated above and which is installed behind the rollers, or by some other separating process not involving any substantial friction, these small cakes are separated or divided into a granular product of the grain fineness already obtained during the preceding deformation, thus without any further grinding effect.

During this grinding process the envelope of the grain, thus the shell, is not cut or ground into small or very small particles. It merely breaks off in fragments of more or less large surface form and retains then a size and shape which allows, in the subsequent sifting operation, without difficulty a separation from the substantially more finely divided endosperm.

By the pressing of the grains between the rollers the natural connection between the endosperm and the shell is destroyed and thus its complete separation by means of the sifting process is made possible.

The substantial preservation of the shell in large size fragments during this grinding process makes it possible to dispense with such a long multiple step crushing operation as practiced heretofore as well as a large portion of the auxiliary means, and carry out the entire grinding process with a substantially smaller investment in machines and apparatus. 7

As example, the following basic arrangement of an installation according to the invention for grinding wheat may be described.

This description refers to the attached drawing giving diagrammatically the essential parts of such an installation.

After the usual pre-cleaning the wheat grains are ground between two smooth rollers 1, which rotate at the same peripheral speed in opposite directions. The gap between the rollers has a width of 0.8 to 1 mm. Thereafter the wheat crushed in this manner is treated in a centrifugal separator 2 of known construction, in which the flour is separated (loosened) from the shell particles by throwing the particles by a rotor to a stationary surrounding wall. The material is now fed to a plane sifter 3 with reciprocating plane sieves, in which the coarse particles, shells and flour parts adhering thereto, are sieved off on the two upper coarser sieves and are fed by ducts 4 and 5 to a second pair of smooth-surface rollers 9 with equal peripheral speed. At 6 and 7 flour is discharged and at 8 the coarser particles on the lower, finer sieves, are discharged and fed to a pair of rollers 25 with smooth surface and equal peripheral speed.

The rollers 9 have a gap with a width of 0.1 to 0.12 mm. and the material falling through is fed to a centrifugal separator 10. From there the material loosened in said separator 10 is fed to the plane sifter 11. The coarser particles separated therein are fed to centrifugal bran finishers 12 and 13, in which a rotor with blades throws the grains on a cylindrical sieve, so that the flour passes the sieve and the bran remains and falls downwards in the cylinder. The flour is fed through 17 and 18 to a centrifugal sifter 20. The bran is discharged through 16 and 19. The flour is separated in the sieve 20 into two fractions of different particle size, which are discharged at 21 and 22, and the bran and the like courser particles remain in the cylindrical sieve and are discharged at 23.

In the plane sifter 11 the finer fractions are discharged through 39 and 40 as fine flour and the particles remaining on the lower, finer plane sieves, are fed through duct 24 together with the particles from duct 8 to the rollers 25. The rollers 25 have a gap with a width of 0.1 to 0.12 mm.

After grinding between these rollers 25 the material is again loosened in a centrifugal separator 26 and is thereafter sifted in a plane sifter 27. The coarser fraction is fed through 28 to the centrifugal bran fiinisher 32 and is separated therein in bran, discharged at 33, and flour. The flour is fed through 34 to a centrifugal sifter 35 with rotating sieve drum. The finest fractions from the sifter 27 are discharged with two different degrees of fineness through 29 and 30. The fraction with dimensions between the coarsest fraction 28 and the finest fractions, 29 and 30, are discharged through 31 and fed to the centrifugal sifter 35, where they are separated into two fractions of flour of different fineness, which are discharged at 21 and 22. The coarser particles, shell parts and contaminations, are discharged at 38 from the interior of the sieve drum through the end face.

In principle the grinding operation could be carried out in a single step but a multiple Step grinding operation as in the example given, has among others the advantage that dust and dirt particles which may be embedded in the furrow or groove of the grains may be removed easier during the sifting process and pass only seldom into the end product.

It should be pointed out that it is known to grind cereal grains in just a few steps and in which the grains are treated in the first step between smooth rollers operating at the same peripheral speed. However, the gap between the rollers is so wide that only the shells are separated from the grain kernel and the kernel itself is not ground or crushed. In a subsequent step the actual grinding operation is carried out between chambered rollers which turn at different peripheral speeds.

The crushing process according to the invention produces furthermore almost no friction heat, but only a deformation heat. The entire heat development is thus considerably less than in the present grinding processes. For this reason the peripheral speed of the rollers and thus their output may be considerably increased, which leads to a further reduction of required machinery for the grinding installation.

The elimination of the friction heat existing in the present grinding processes brings about also a considerable saving in energy consumption. The heating of the grains or flour arises in a considerably less degree and thus causes also a much reduced evaporation loss. The danger of condensation with its disadvantageous consequences is also eliminated since the grinding at the same humidity content of the end product may take place with considerably less humidity content in the raw material.

The flour obtained with this process is rougher to the touch. The removal of the germ bud during the grinding process is also facilitated considerably as it is no longer cut and crushed as before, but is merely flattened, and thus may be separated more easily and to a larger extent. Its enzymes and fermentation ingredients as well as those of the other shell components get into the endosperm product only to a small degree and therefore cannot impair their utilitarian properties any longer.

The drive of both rollers of an indivdual pair, thus the usual gear and chain transmission employed until now is no longer necessary, because the second roller may easily operate as a so-called drag roller which brings about a simplification of the roller frame construction.

As may be seen from the above explanations individual 6 crushing steps of this novel grinding process are characterized by the following work processes:

(1) The deformation of the cereal grains produced exclusively by a pressing operation obtained by passing the grains between the smooth rollers and due to the fact that the individual rollers turn at the same speed.

(2) The separation of the ground material obtained from the rollers substantially in the form of flat bodies consisting of endosperm and shell components by means of centrifugal or similar separators.

(3) The sifting of the ground material received from the centrifugal separators in grain fractions, consisting of pure flour or very fine flour and coarser shell particles with attached endosperm particles. These last-named fractions which, by the way, differ to a very large degre from the structure, dimension, and form of those obtained in the present grinding processes, such as coarse grit, grit sernolina and dust, are further crushed and separated in a working operation which may be repeated and in which the gap between the rollers is successively reduced, as indicated above, until the endosperm is separated completely from the envelope, the shell with all its components, and is pulverized and separated to the desired grain size or fineness.

It may be seen that this grinding process as already mentioned requires very few steps to obtain the final disintegration of the endosperm into flour because the shell, in contrast to the presently known operations, is preserved in this novel working process in fragments of relatively large surface and may therefore be separated more easily during the sifting operation from the endosperm products of smaller grain size. The flour obtained thus has a much smaller ash content so that the same yield has a lighter color than before.

The residue of this grinding operation, the shell com ponents, may the same is in the known grain milling operations be thereafter liberated of any endosperm particles which may still be attached thereto by means of so-called bran brushes or centrifugal apparatus. The endosperm particles obtained in this manner may, depending on their nature or purity, be ultimately added to the flour or they provide a feed flour in case of excessive ash content in receiving a corresponding increase of shell particles of the same grain size during this last working phase.

What is claimed is:

1. Apparatus for grinding cereal grains and like shell covered fruits comprising in combination,

a first set of at least one pair of rollers having a smooth peripheral surface and rotatable at approximately the same peripheral speed,

said rollers of said first set of roller pairs being adjusted to provide between each pair of rollers a gap having a width smaller than the smallest dimension of the grains to produce flattened grains having a pressed dimension larger than the size of the end product,

a second set of at least one pair of rollers having a smooth peripheral surface and rotatable at approximately the same peripheral speed,

said rollers of said second set of roller pairs being adjusted to provide between each pair of rollers a gap having a width to produce grain bodies having a pressed dimension of the size of the end product,

means for conducting said flattened grains from said first set of rollers to said second set of rollers,

means for centrifugally subdividing said grain bodies into individual grain particles,

and means for sifting said subdivided grain particles to separate the endosperm grain particles from the shell grain particles.

2. A process for grinding cereal grains and like shell covered fruits and separating the shells from the endosperm comprising the steps of passing the grains between at least one pair of rollers having a smooth peripheral surface,

rotating said rollers at approximately the same peripheral speed,

compressing said grains between said rollers into substantially fiat bodies consisting of shell components and endosperm particles of the desired granular size of the end product, and

conducting said shell components and said endosperm particles through separator means for separating said shell components from said endosperm particles.

3. A process for grinding cereal grains and like shell covered fruits and separating the shells from the endo sperm comprising the steps of passing the grains between at least one pair of rollers having a smooth peripheral surface,

rotating said rollers at approximately the same speed,

compressing said grains between said rollers into substantially flat bodies consisting of shell particles and endosperm particles of the desired granular size of the end product, conducting said shell and endosperm particles through centrifugal separator means for separating'said shell particles from said endosperm particles,

separating the coarse shell and endosperm particles in a sifting device,

passing these coarse shell and endosperm particles between at least one other pair of rollers having a smooth peripheral surface and rotating at approximately the same peripheral speed, and separating the shell and endosperm particles from said other pair of rollers in another centrifugal separator.

4. A process according to claim 3 including passing the shell and endosperm particles from said centrifugal separator into another sifting device and conducting sifted particles of a selected size between additional rollers rotating at approximately the same speed.

5. Apparatus for milling cereal grains and like shell covered fruits comprising at least one pair of pressing rollers having a smooth peripheral surface and rotatable at approximately the same peripheral speed.

said rollers being adjusted to provide between the pair of rollers a gap having a width which will cause the rollers to compress the grain suificiently to reduce the endosperm to a desired particle size, break the grain shell into fragments of larger size than said endo sperm, and compact at least a portion of said deformed endosperm and said fragmented shell into a substantially fiat body, said width being substantially smaller than the smallest dimension of the grains.

6. The apparatus of claim 5 including means for subdividing said compacted grains into individual grain particles.

7. The apparatus of claim 6 including sifting means for separating the endosperm particles from the shell particles.

References Cited by the Examiner UNITED STATES PATENTS 1,784,762 12/1930 Smith 24l11 2,392,365 1/1946 Carter 241ll X 2,464,212 3/1949 Carter et al. 24111 X ROBERT C. RIORDON, Primary Examiner.

J. SPENCER OVERHOLSER, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,226,041 December 28, 1965 Hermann Graumann It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant (only) for "Hermann Grauman" read Hermann Graumann column 2, line 42, for "previousy" read previously column 5, line 1, for "courser" read for "chambered" read chamfered coarser line 41,

Signed and sealed this 6th day of December 1966.

(SEAL) ERNEST W. SW'IDER Attest:

EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

2. A PROCESS FRO GRINDLING CEREAL GRAINS AND LIKE SHELL COVERED FRUTS AND SEPARATING THE SHELLS FROM THE ENDOSPERM COMPRISING THE STEPS OF PASSING THE GRAINS BETWEEN AT LEAST ONE PAIR OF ROLLERS HAVING A SMOOTH PERIPHERAL SURFACE, ROTATING SAID ROLLERS AT APPROXIMATELY THE SAME PERIPHERAL SPEED, COMPRESSING SAID GRAINS BETWEEN SAID ROLLERS INTO SUBSTANTIALLY FLAT BODIES CONSISTING OF SHEEL COMPONENTS AND ENDOSPERM PARTICLES OF THE DESICRED GRANULAR SIZE OF THE END PRODUCT, AND CONDUCTING SAID SHELL COMPONENTS AND SAID ENDOSPERM PARTICLES THROUGH SEPARATOR MEANS FOR SEPARATING SAID SHELL COMPONENTS FROM AID ENDOSPERM PARTICLES,
 5. APPARATUS FOR MILLING CEREAL GRAINS AND LIKE SHELL COVERED FRUITS COMPRISING AT LEAST ONE PAIR PRESSING ROLLERS HAVING A SMOOTH PERIPHERAL SURFACE AND ROTATABLE AT APPROXIMATELY THE SAME PERIPHERAL SPEED. SAID ROLLERS BEING ADJUSTED TO PROVIDE BETWEEN THE PAIR OF ROLLERS A GAP HAVING A WIDTH WHICH WILL CAUSE THE ROLLERS TO COMPRESS THE GRAIN SUFFICIENTLY TO REDUCE THE ENDOSPERM TO A DESIRED PARTICLE SIZE, BREAK THE GRAIN SHELL INTO FRAGMENTS OF LARGER SIZE THAN SAID ENDOSPERM, AND COMPACT AT LEAST A PORTION OF SAID DEFORMED ENDOSPERM AND SAID FRAGMENTED SHELL INTO A SUBSTANTIALLY FLAT BODY, SAID WIDTH BEING SUBSTANTIALLY SMALLER THAN THE SMALLEST DIMENSION OF THE GRAINS. 